The present invention relates to burner nozzle tips adapted for use in pulverized-coal fired furnaces and, more particularly, to a nozzle tip for pulverized coal-fired burner having a replaceable cast insert of highly abrasion resistant material and a replaceable end cap of temperature resistant material.
One common method of firing coal in conventional coal-fired steam generating boiler furnaces is known as tangential firing. In this method pulverized coal is introduced into the furnace in a primary air stream through burners, frequently termed fuel-air admission assemblies, located in the corner windboxes of the furnace. The pulverized coal-air streams discharging from these burners are aimed tangentially to an imaginary circle in the middle of the furnace to create a massive flame therein termed a fireball.
Upon leaving the furnace proper, the combustion products formed in the fireball pass through a boiler section typically housing a superheater, a reheater, and other various heat absorption surfaces to cool the combustion products and generate superheated steam. By changing the position of the fireball formed in the furnace upon convergence of the fuel-air streams emanating from the burners, control of the temperature of the steam leaving the superheater or reheater is achieved. By tilting the burner nozzle tips in unison the fireball can be physically raised or lowered within the furnace so as to increase or decrease the heat absorption of the furnace waterwalls thereby raising or lowering the temperature of the combustion products leaving the furnace proper and passing over the superheater and reheater surface. As the temperature of the combustion products entering the boiler section changes, the temperature of the steam generated in the heat absorption surface disposed therein changes proportionately. Such a method of steam temperature control is shown in U.S. Pat. No. 2,363,875 to Kreisinger et al.
A typical coal-air admission assembly or burner employed heretofore on tangentially-fired furnaces comprises a coal delivery pipe, often termed a coal nozzle, through which pulverized coal entrained in a primary air stream is delivered to the furnace, an air conduit surrounding the coal delivery pipe through which additional air is delivered to the furnace, and a nozzle tip pivotally mounted to the coal delivery pipe so as to be tiltable in a vertical plane whereby the pulverized coal-air stream being delivered to the furnace through the coal delivery pipe and the additional air passing through the air conduit can be selectively directed into the furnace as dictated by steam temperature requirements.
A typical prior art burner nozzle tip, such as that shown in U.S. Pat. No. 2,895,435 to Bogot et al, was formed of a steel open-ended inner shell defining a flow passage through which the pulverized coal-air stream from the coal delivery pipe is delivered into the furnace and a steel open-ended outer shell spaced from and surrounding the inner shell so as to define therebetween an annular duct through which the air leaving the air conduit is directed into the furnace. Additionally, one or more steel or stainless steel baffles, termed splitter plates, are typically disposed within the inner shell of the nozzle tip and aligned parallel to the longitudinal axis thereof, to impart additional directional force to the coal-air stream discharging through the inner shell and to insure a uniform distribution of the coal-air stream particularly when the nozzle is tilted away from the horizontal for steam temperature control.
A major problem heretofore encountered in using such nozzle tips has been the rapid wear of the steel or stainless steel splitter plates due to extreme erosion caused by the impingement of coal particles entrained in the high velocity air stream passing from the coal delivery pipe. As these splitter plates wear away, they lose their ability to adequately direct the pulverized-coal air stream into the furnace, thus detracting from the effectiveness of the tip. Additionally, coal particles impinge upon the walls of the inner shell when the nozzle tips are tilted away from the horizontal resulting in increased and more rapid wear of the inner shell itself.
The nozzle tip is also exposed to heat from the flame in the furnace. Prior art nozzle tips have been susceptible to cracking due to exposure to this heat particularly where the splitter plates are welded to the inner shell or where the inner shell is welded to the outer shell.
A burner nozzle tip is disclosed in U.S. Pat. No. 3,823,875 which is alleged to overcome the aforementioned problems by providing a burner nozzle tip which is formed of an outer shell of particularly heat resistant stainless steel and an inner shell of particularly erosion resistant stainless steel both of which are fabricated by casting and not welding and which are assembled and held together mechanically to form the nozzle tip rather than being welded together. In order to replace the inner shell, which although made of a more erosion resistant stainless steel still must be replaced sooner than the outer shell, the nozzle tip must be completely removed from the coal nozzle itself and the inner shell pulled rearwardly from the outer shell. Then a new inner shell must be inserted within the outer shell and the entire coal nozzle tip again attached to the coal nozzle. This is a cumbersome and time-consuming operation which, as it must be done when the furnace is out of operation, may unnecessarily extend the downtime of the furnace.
Therefore, it is an object of the present invention to provide an improved nozzle tip for a pulverized coal-fired burner which incorporates a replaceable highly erosion resistant insert that defines a flow passage for directing pulverized coal entrained in primary air from the coal delivery pipe into the furnace and a replaceable highly temperature resistant end cap which is mounted to the end of the nozzle tip exposed to the high temperatures generated within the furnace.
It is a further object of the present invention to provide such an improved burner nozzle tip which is readily disassembleable from the interior of the furnace without detaching the entire nozzle tip body from the coal delivery pipe of the burner.
It is still another object of the present invention to provide a replaceable, weld-free, cast insert of highly abrasion resistant material and a replaceable end cap of highly temperature resistant material adapted to mate with the nozzle tip body and be secured thereto by mechanical means rather than welding.